AVR-Chat

Hi

I am currently driving an AVR (mega 8) input from a SFH618A 
optoisolator being driven from the output of a radio control 
receiver. The input LED is driven from the R/C receiver via a 330R 
series resistor and the output transistors emmitter is taken to 
ground with a 3K3 resistor. The transistor collector is taken to +5V 
and to AVR is driven directly from the transistor emmitter pin. The 
LED is connected to ground on the R/C receiver. This works fine.

The problem is that I cannot find any other optoisolator that will 
work in this circuit and cannot find any new resistor values to work 
with the other optoisolators I have, (e.g SFH615, TLP504). The 
SFH618 is relatively expensive you see.

Can anyone recommend a good way of choosing resistor values or point 
me to a good "how to use optoisolator" type article please?

Mark